
package java_cup.runtime;

import java.util.Stack;

/**
 * This class implements a skeleton table driven LR parser. In general, LR
 * parsers are a form of bottom up shift-reduce parsers. Shift-reduce parsers
 * act by shifting input onto a parse stack until the Symbols matching the right
 * hand side of a production appear on the top of the stack. Once this occurs, a
 * reduce is performed. This involves removing the Symbols corresponding to the
 * right hand side of the production (the so called "handle") and replacing them
 * with the non-terminal from the left hand side of the production.
 * <p>
 * To control the decision of whether to shift or reduce at any given point, the
 * parser uses a state machine (the "viable prefix recognition machine" built by
 * the parser generator). The current state of the machine is placed on top of
 * the parse stack (stored as part of a Symbol object representing a terminal or
 * non terminal). The parse action table is consulted (using the current state
 * and the current lookahead Symbol as indexes) to determine whether to shift or
 * to reduce. When the parser shifts, it changes to a new state by pushing a new
 * Symbol (containing a new state) onto the stack. When the parser reduces, it
 * pops the handle (right hand side of a production) off the stack. This leaves
 * the parser in the state it was in before any of those Symbols were matched.
 * Next the reduce-goto table is consulted (using the new state and current
 * lookahead Symbol as indexes) to determine a new state to go to. The parser
 * then shifts to this goto state by pushing the left hand side Symbol of the
 * production (also containing the new state) onto the stack.
 * <p>
 * This class actually provides four LR parsers. The methods parse() and
 * debug_parse() provide two versions of the main parser (the only difference
 * being that debug_parse() emits debugging trace messages as it parses). In
 * addition to these main parsers, the error recovery mechanism uses two more.
 * One of these is used to simulate "parsing ahead" in the input without
 * carrying out actions (to verify that a potential error recovery has worked),
 * and the other is used to parse through buffered "parse ahead" input in order
 * to execute all actions and re-synchronize the actual parser configuration.
 * <p>
 * This is an abstract class which is normally filled out by a subclass
 * generated by the JavaCup parser generator. In addition to supplying the
 * actual parse tables, generated code also supplies methods which invoke
 * various pieces of user supplied code, provide access to certain special
 * Symbols (e.g., EOF and error), etc. Specifically, the following abstract
 * methods are normally supplied by generated code: <dl compact>
 * <dt>short[][] production_table()
 * <dd>Provides a reference to the production table (indicating the index of the
 * left hand side non terminal and the length of the right hand side for each
 * production in the grammar).
 * <dt>short[][] action_table()
 * <dd>Provides a reference to the parse action table.
 * <dt>short[][] reduce_table()
 * <dd>Provides a reference to the reduce-goto table.
 * <dt>int start_state()
 * <dd>Indicates the index of the start state.
 * <dt>int start_production()
 * <dd>Indicates the index of the starting production.
 * <dt>int EOF_sym()
 * <dd>Indicates the index of the EOF Symbol.
 * <dt>int error_sym()
 * <dd>Indicates the index of the error Symbol.
 * <dt>Symbol do_action()
 * <dd>Executes a piece of user supplied action code. This always comes at the
 * point of a reduce in the parse, so this code also allocates and fills in the
 * left hand side non terminal Symbol object that is to be pushed onto the stack
 * for the reduce.
 * <dt>void init_actions()
 * <dd>Code to initialize a special object that encapsulates user supplied
 * actions (this object is used by do_action() to actually carry out the
 * actions).
 * </dl>
 * In addition to these routines that <i>must</i> be supplied by the generated
 * subclass there are also a series of routines that <i>may</i> be supplied.
 * These include:
 * <dl>
 * <dt>Symbol scan()
 * <dd>Used to get the next input Symbol from the scanner.
 * <dt>Scanner getScanner()
 * <dd>Used to provide a scanner for the default implementation of scan().
 * <dt>int error_sync_size()
 * <dd>This determines how many Symbols past the point of an error must be
 * parsed without error in order to consider a recovery to be valid. This
 * defaults to 3. Values less than 2 are not recommended.
 * <dt>void report_error(String message, Object info)
 * <dd>This method is called to report an error. The default implementation
 * simply prints a message to System.err and where the error occurred. This
 * method is often replaced in order to provide a more sophisticated error
 * reporting mechanism.
 * <dt>void report_fatal_error(String message, Object info)
 * <dd>This method is called when a fatal error that cannot be recovered from is
 * encountered. In the default implementation, it calls report_error() to emit a
 * message, then throws an exception.
 * <dt>void syntax_error(Symbol cur_token)
 * <dd>This method is called as soon as syntax error is detected (but before
 * recovery is attempted). In the default implementation it invokes:
 * report_error("Syntax error", null);
 * <dt>void unrecovered_syntax_error(Symbol cur_token)
 * <dd>This method is called if syntax error recovery fails. In the default
 * implementation it invokes:<br>
 * report_fatal_error("Couldn't repair and continue parse", null);
 * </dl>
 *
 * @see Symbol
 * @see Symbol
 * @see virtual_parse_stack
 * @version last updated: 7/3/96
 * @author Frank Flannery
 */
@SuppressWarnings("unchecked" )
public abstract class lr_parser {
    /*-----------------------------------------------------------*/
    /*--- Constructor(s) ----------------------------------------*/
    /*-----------------------------------------------------------*/

    /**
     * Simple constructor.
     */
    public lr_parser() {
        symbolFactory = new DefaultSymbolFactory();
    }

    /**
     * Constructor that sets the default scanner. [CSA/davidm]
     */
    public lr_parser(Scanner s) {
        this(s, new DefaultSymbolFactory()); // TUM 20060327 old cup v10 Symbols
                                            // as default
    }

    /**
     * Constructor that sets the default scanner and a SymbolFactory
     */
    public lr_parser(Scanner s, SymbolFactory symfac) {
        this(); // in case default constructor someday does something
        symbolFactory = symfac;
        setScanner(s);
    }

    public SymbolFactory symbolFactory;// = new DefaultSymbolFactory();

    /**
     * Whenever creation of a new Symbol is necessary, one should use this factory.
     */
    public SymbolFactory getSymbolFactory() {
        return symbolFactory;
    }
    /*-----------------------------------------------------------*/
    /*--- (Access to) Static (Class) Variables ------------------*/
    /*-----------------------------------------------------------*/

    /**
     * The default number of Symbols after an error we much match to consider it
     * recovered from.
     */
    protected final static int _error_sync_size = 3;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * The number of Symbols after an error we much match to consider it recovered
     * from.
     */
    protected int error_sync_size() {
        return _error_sync_size;
    }

    /*-----------------------------------------------------------*/
    /*--- (Access to) Instance Variables ------------------------*/
    /*-----------------------------------------------------------*/

    /**
     * Table of production information (supplied by generated subclass). This table
     * contains one entry per production and is indexed by the negative-encoded
     * values (reduce actions) in the action_table. Each entry has two parts, the
     * index of the non-terminal on the left hand side of the production, and the
     * number of Symbols on the right hand side.
     */
    public abstract short[][] production_table();

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * The action table (supplied by generated subclass). This table is indexed by
     * state and terminal number indicating what action is to be taken when the
     * parser is in the given state (i.e., the given state is on top of the stack)
     * and the given terminal is next on the input. States are indexed using the
     * first dimension, however, the entries for a given state are compacted and
     * stored in adjacent index, value pairs which are searched for rather than
     * accessed directly (see get_action()). The actions stored in the table will be
     * either shifts, reduces, or errors. Shifts are encoded as positive values (one
     * greater than the state shifted to). Reduces are encoded as negative values
     * (one less than the production reduced by). Error entries are denoted by zero.
     *
     * @see lr_parser#get_action
     */
    public abstract short[][] action_table();

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * The reduce-goto table (supplied by generated subclass). This table is indexed
     * by state and non-terminal number and contains state numbers. States are
     * indexed using the first dimension, however, the entries for a given state are
     * compacted and stored in adjacent index, value pairs which are searched for
     * rather than accessed directly (see get_reduce()). When a reduce occurs, the
     * handle (corresponding to the RHS of the matched production) is popped off the
     * stack. The new top of stack indicates a state. This table is then indexed by
     * that state and the LHS of the reducing production to indicate where to
     * "shift" to.
     *
     * @see lr_parser#get_reduce
     */
    public abstract short[][] reduce_table();

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * The index of the start state (supplied by generated subclass).
     */
    public abstract int start_state();

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * The index of the start production (supplied by generated subclass).
     */
    public abstract int start_production();

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * The index of the end of file terminal Symbol (supplied by generated
     * subclass).
     */
    public abstract int EOF_sym();

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * The index of the special error Symbol (supplied by generated subclass).
     */
    public abstract int error_sym();

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /** Internal flag to indicate when parser should quit. */
    protected boolean _done_parsing = false;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * This method is called to indicate that the parser should quit. This is
     * normally called by an accept action, but can be used to cancel parsing early
     * in other circumstances if desired.
     */
    public void done_parsing() {
        _done_parsing = true;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */
    /*
     * Global parse state shared by parse(), error recovery, and debugging routines
     */
    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Indication of the index for top of stack (for use by actions).
     */
    protected int       tos;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /** The current lookahead Symbol. */
    protected Symbol    cur_token;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /** The parse stack itself. */
    protected Stack     stack = new Stack();

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /** Direct reference to the production table. */
    protected short[][] production_tab;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /** Direct reference to the action table. */
    protected short[][] action_tab;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /** Direct reference to the reduce-goto table. */
    protected short[][] reduce_tab;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * This is the scanner object used by the default implementation of scan() to
     * get Symbols. To avoid name conflicts with existing code, this field is
     * private. [CSA/davidm]
     */
    private Scanner     _scanner;

    /**
     * Simple accessor method to set the default scanner.
     */
    public void setScanner(Scanner s) {
        _scanner = s;
    }

    /**
     * Simple accessor method to get the default scanner.
     */
    public Scanner getScanner() {
        return _scanner;
    }

    /*-----------------------------------------------------------*/
    /*--- General Methods ---------------------------------------*/
    /*-----------------------------------------------------------*/

    /**
     * Perform a bit of user supplied action code (supplied by generated subclass).
     * Actions are indexed by an internal action number assigned at parser
     * generation time.
     *
     * @param act_num the internal index of the action to be performed.
     * @param parser the parser object we are acting for.
     * @param stack the parse stack of that object.
     * @param top the index of the top element of the parse stack.
     */
    public abstract Symbol do_action(int act_num, lr_parser parser, Stack stack, int top) throws java.lang.Exception;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * User code for initialization inside the parser. Typically this initializes
     * the scanner. This is called before the parser requests the first Symbol. Here
     * this is just a placeholder for subclasses that might need this and we perform
     * no action. This method is normally overridden by the generated code using
     * this contents of the "init with" clause as its body.
     */
    public void user_init() throws java.lang.Exception {}

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Initialize the action object. This is called before the parser does any parse
     * actions. This is filled in by generated code to create an object that
     * encapsulates all action code.
     */
    protected abstract void init_actions() throws java.lang.Exception;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Get the next Symbol from the input (supplied by generated subclass). Once end
     * of file has been reached, all subsequent calls to scan should return an EOF
     * Symbol (which is Symbol number 0). By default this method returns
     * getScanner().next_token(); this implementation can be overriden by the
     * generated parser using the code declared in the "scan with" clause. Do not
     * recycle objects; every call to scan() should return a fresh object.
     */
    public Symbol scan() throws java.lang.Exception {
        Symbol sym = getScanner().next_token();
        return (sym != null) ? sym : getSymbolFactory().newSymbol("END_OF_FILE", EOF_sym());
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Report a fatal error. This method takes a message string and an additional
     * object (to be used by specializations implemented in subclasses). Here in the
     * base class a very simple implementation is provided which reports the error
     * then throws an exception.
     *
     * @param message an error message.
     * @param info an extra object reserved for use by specialized subclasses.
     */
    public void report_fatal_error(String message, Object info) throws java.lang.Exception {
        /*
         * stop parsing (not really necessary since we throw an exception, but)
         */
        done_parsing();

        /*
         * use the normal error message reporting to put out the message
         */
        report_error(message, info);

        /* throw an exception */
        throw new Exception("Can't recover from previous error(s)");
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Report a non fatal error (or warning). This method takes a message string and
     * an additional object (to be used by specializations implemented in
     * subclasses). Here in the base class a very simple implementation is provided
     * which simply prints the message to System.err.
     *
     * @param message an error message.
     * @param info an extra object reserved for use by specialized subclasses.
     */
    public void report_error(String message, Object info) {
        System.err.print(message);
        System.err.flush();
        if (info instanceof Symbol)
            if (((Symbol) info).left != -1)
                System.err.println(" at character " + ((Symbol) info).left + " of input");
            else
                System.err.println("");
        else
            System.err.println("");
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * This method is called when a syntax error has been detected and recovery is
     * about to be invoked. Here in the base class we just emit a "Syntax error"
     * error message.
     *
     * @param cur_token the current lookahead Symbol.
     */
    public void syntax_error(Symbol cur_token) throws Exception {
        report_error("Syntax error", cur_token);
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * This method is called if it is determined that syntax error recovery has been
     * unsuccessful. Here in the base class we report a fatal error.
     *
     * @param cur_token the current lookahead Symbol.
     */
    public void unrecovered_syntax_error(Symbol cur_token) throws java.lang.Exception {
        report_fatal_error("Couldn't repair and continue parse", cur_token);
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Fetch an action from the action table. The table is broken up into rows, one
     * per state (rows are indexed directly by state number). Within each row, a
     * list of index, value pairs are given (as sequential entries in the table),
     * and the list is terminated by a default entry (denoted with a Symbol index of
     * -1). To find the proper entry in a row we do a linear or binary search
     * (depending on the size of the row).
     *
     * @param state the state index of the action being accessed.
     * @param sym the Symbol index of the action being accessed.
     */
    protected final short get_action(int state, int sym) {
        short tag;
        int first, last, probe;
        short[] row = action_tab[state];

        /* linear search if we are < 10 entries */
        if (row.length < 20)
            for (probe = 0; probe < row.length; probe++) {
                /* is this entry labeled with our Symbol or the default? */
                tag = row[probe++];
                if (tag == sym || tag == -1) {
                    /* return the next entry */
                    return row[probe];
                }
            }
        /* otherwise binary search */
        else {
            first = 0;
            last = (row.length - 1) / 2 - 1; /* leave out trailing default entry */
            while (first <= last) {
                probe = (first + last) / 2;
                if (sym == row[probe * 2])
                    return row[probe * 2 + 1];
                else if (sym > row[probe * 2])
                    first = probe + 1;
                else
                    last = probe - 1;
            }

            /* not found, use the default at the end */
            return row[row.length - 1];
        }

        /*
         * shouldn't happened, but if we run off the end we return the default (error ==
         * 0)
         */
        return 0;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Fetch a state from the reduce-goto table. The table is broken up into rows,
     * one per state (rows are indexed directly by state number). Within each row, a
     * list of index, value pairs are given (as sequential entries in the table),
     * and the list is terminated by a default entry (denoted with a Symbol index of
     * -1). To find the proper entry in a row we do a linear search.
     *
     * @param state the state index of the entry being accessed.
     * @param sym the Symbol index of the entry being accessed.
     */
    protected final short get_reduce(int state, int sym) {
        short tag;
        short[] row = reduce_tab[state];

        /* if we have a null row we go with the default */
        if (row == null)
            return -1;

        for (int probe = 0; probe < row.length; probe++) {
            /* is this entry labeled with our Symbol or the default? */
            tag = row[probe++];
            if (tag == sym || tag == -1) {
                /* return the next entry */
                return row[probe];
            }
        }
        /*
         * if we run off the end we return the default (error == -1)
         */
        return -1;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * This method provides the main parsing routine. It returns only when
     * done_parsing() has been called (typically because the parser has accepted, or
     * a fatal error has been reported). See the header documentation for the class
     * regarding how shift/reduce parsers operate and how the various tables are
     * used.
     */
    public Symbol parse() throws java.lang.Exception {
        /* the current action code */
        int act;

        /* the Symbol/stack element returned by a reduce */
        Symbol lhs_sym = null;

        /* information about production being reduced with */
        short handle_size, lhs_sym_num;

        /* set up direct reference to tables to drive the parser */

        production_tab = production_table();
        action_tab = action_table();
        reduce_tab = reduce_table();

        /* initialize the action encapsulation object */
        init_actions();

        /* do user initialization */
        user_init();

        /* get the first token */
        cur_token = scan();

        /* push dummy Symbol with start state to get us underway */
        stack.removeAllElements();
        stack.push(getSymbolFactory().startSymbol("START", 0, start_state()));
        tos = 0;

        /* continue until we are told to stop */
        for (_done_parsing = false; !_done_parsing;) {
            /* Check current token for freshness. */
            if (cur_token.used_by_parser)
                throw new Error("Symbol recycling detected (fix your scanner).");

            /* current state is always on the top of the stack */

            /*
             * look up action out of the current state with the current input
             */
            act = get_action(((Symbol) stack.peek()).parse_state, cur_token.sym);

            /* decode the action -- > 0 encodes shift */
            if (act > 0) {
                /* shift to the encoded state by pushing it on the stack */
                cur_token.parse_state = act - 1;
                cur_token.used_by_parser = true;
                stack.push(cur_token);
                tos++;

                /* advance to the next Symbol */
                cur_token = scan();
            }
            /* if its less than zero, then it encodes a reduce action */
            else if (act < 0) {
                /* perform the action for the reduce */
                lhs_sym = do_action((-act) - 1, this, stack, tos);

                /* look up information about the production */
                lhs_sym_num = production_tab[(-act) - 1][0];
                handle_size = production_tab[(-act) - 1][1];

                /* pop the handle off the stack */
                for (int i = 0; i < handle_size; i++) {
                    stack.pop();
                    tos--;
                }

                /* look up the state to go to from the one popped back to */
                act = get_reduce(((Symbol) stack.peek()).parse_state, lhs_sym_num);

                /* shift to that state */
                lhs_sym.parse_state = act;
                lhs_sym.used_by_parser = true;
                stack.push(lhs_sym);
                tos++;
            }
            /* finally if the entry is zero, we have an error */
            else if (act == 0) {
                /* call user syntax error reporting routine */
                syntax_error(cur_token);

                /* try to error recover */
                if (!error_recovery(false)) {
                    /* if that fails give up with a fatal syntax error */
                    unrecovered_syntax_error(cur_token);

                    /* just in case that wasn't fatal enough, end parse */
                    done_parsing();
                } else {
                    lhs_sym = (Symbol) stack.peek();
                }
            }
        }
        return lhs_sym;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Write a debugging message to System.err for the debugging version of the
     * parser.
     *
     * @param mess the text of the debugging message.
     */
    public void debug_message(String mess) {
        System.err.println(mess);
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /** Dump the parse stack for debugging purposes. */
    public void dump_stack() {
        if (stack == null) {
            debug_message("# Stack dump requested, but stack is null");
            return;
        }

        debug_message("============ Parse Stack Dump ============");

        /* dump the stack */
        for (int i = 0; i < stack.size(); i++) {
            debug_message("Symbol: " + ((Symbol) stack.elementAt(i)).sym + " State: " + ((Symbol) stack.elementAt(i)).parse_state);
        }
        debug_message("==========================================");
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Do debug output for a reduce.
     *
     * @param prod_num the production we are reducing with.
     * @param nt_num the index of the LHS non terminal.
     * @param rhs_size the size of the RHS.
     */
    public void debug_reduce(int prod_num, int nt_num, int rhs_size) {
        debug_message("# Reduce with prod #" + prod_num + " [NT=" + nt_num + ", " + "SZ=" + rhs_size + "]");
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Do debug output for shift.
     *
     * @param shift_tkn the Symbol being shifted onto the stack.
     */
    public void debug_shift(Symbol shift_tkn) {
        debug_message("# Shift under term #" + shift_tkn.sym + " to state #" + shift_tkn.parse_state);
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Do debug output for stack state. [CSA]
     */
    public void debug_stack() {
        StringBuffer sb = new StringBuffer("## STACK:");
        for (int i = 0; i < stack.size(); i++) {
            Symbol s = (Symbol) stack.elementAt(i);
            sb.append(" <state " + s.parse_state + ", sym " + s.sym + ">");
            if ((i % 3) == 2 || (i == (stack.size() - 1))) {
                debug_message(sb.toString());
                sb = new StringBuffer("         ");
            }
        }
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Perform a parse with debugging output. This does exactly the same things as
     * parse(), except that it calls debug_shift() and debug_reduce() when shift and
     * reduce moves are taken by the parser and produces various other debugging
     * messages.
     */
    public Symbol debug_parse() throws java.lang.Exception {
        /* the current action code */
        int act;

        /* the Symbol/stack element returned by a reduce */
        Symbol lhs_sym = null;

        /* information about production being reduced with */
        short handle_size, lhs_sym_num;

        /* set up direct reference to tables to drive the parser */
        production_tab = production_table();
        action_tab = action_table();
        reduce_tab = reduce_table();

        debug_message("# Initializing parser");

        /* initialize the action encapsulation object */
        init_actions();

        /* do user initialization */
        user_init();

        /* the current Symbol */
        cur_token = scan();

        debug_message("# Current Symbol is #" + cur_token.sym);

        /* push dummy Symbol with start state to get us underway */
        stack.removeAllElements();
        stack.push(getSymbolFactory().startSymbol("START", 0, start_state()));
        tos = 0;

        /* continue until we are told to stop */
        for (_done_parsing = false; !_done_parsing;) {
            /* Check current token for freshness. */
            if (cur_token.used_by_parser)
                throw new Error("Symbol recycling detected (fix your scanner).");

            /* current state is always on the top of the stack */
            // debug_stack();

            /*
             * look up action out of the current state with the current input
             */
            act = get_action(((Symbol) stack.peek()).parse_state, cur_token.sym);

            /* decode the action -- > 0 encodes shift */
            if (act > 0) {
                /* shift to the encoded state by pushing it on the stack */
                cur_token.parse_state = act - 1;
                cur_token.used_by_parser = true;
                debug_shift(cur_token);
                stack.push(cur_token);
                tos++;

                /* advance to the next Symbol */
                cur_token = scan();
                debug_message("# Current token is " + cur_token);
            }
            /* if its less than zero, then it encodes a reduce action */
            else if (act < 0) {
                /* perform the action for the reduce */
                lhs_sym = do_action((-act) - 1, this, stack, tos);

                /* look up information about the production */
                lhs_sym_num = production_tab[(-act) - 1][0];
                handle_size = production_tab[(-act) - 1][1];

                debug_reduce((-act) - 1, lhs_sym_num, handle_size);

                /* pop the handle off the stack */
                for (int i = 0; i < handle_size; i++) {
                    stack.pop();
                    tos--;
                }

                /* look up the state to go to from the one popped back to */
                act = get_reduce(((Symbol) stack.peek()).parse_state, lhs_sym_num);
                debug_message("# Reduce rule: top state " + ((Symbol) stack.peek()).parse_state + ", lhs sym " + lhs_sym_num + " -> state " + act);

                /* shift to that state */
                lhs_sym.parse_state = act;
                lhs_sym.used_by_parser = true;
                stack.push(lhs_sym);
                tos++;

                debug_message("# Goto state #" + act);
            }
            /* finally if the entry is zero, we have an error */
            else if (act == 0) {
                /* call user syntax error reporting routine */
                syntax_error(cur_token);

                /* try to error recover */
                if (!error_recovery(true)) {
                    /* if that fails give up with a fatal syntax error */
                    unrecovered_syntax_error(cur_token);

                    /* just in case that wasn't fatal enough, end parse */
                    done_parsing();
                } else {
                    lhs_sym = (Symbol) stack.peek();
                }
            }
        }
        return lhs_sym;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */
    /* Error recovery code */
    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Attempt to recover from a syntax error. This returns false if recovery fails,
     * true if it succeeds. Recovery happens in 4 steps. First we pop the parse
     * stack down to a point at which we have a shift out of the top-most state on
     * the error Symbol. This represents the initial error recovery configuration.
     * If no such configuration is found, then we fail. Next a small number of
     * "lookahead" or "parse ahead" Symbols are read into a buffer. The size of this
     * buffer is determined by error_sync_size() and determines how many Symbols
     * beyond the error must be matched to consider the recovery a success. Next, we
     * begin to discard Symbols in attempt to get past the point of error to a point
     * where we can continue parsing. After each Symbol, we attempt to "parse ahead"
     * though the buffered lookahead Symbols. The "parse ahead" process simulates
     * that actual parse, but does not modify the real parser's configuration, nor
     * execute any actions. If we can parse all the stored Symbols without error,
     * then the recovery is considered a success. Once a successful recovery point
     * is determined, we do an actual parse over the stored input -- modifying the
     * real parse configuration and executing all actions. Finally, we return the
     * the normal parser to continue with the overall parse.
     *
     * @param debug should we produce debugging messages as we parse.
     */
    protected boolean error_recovery(boolean debug) throws java.lang.Exception {
        if (debug)
            debug_message("# Attempting error recovery");

        /*
         * first pop the stack back into a state that can shift on error and do that
         * shift (if that fails, we fail)
         */
        if (!find_recovery_config(debug)) {
            if (debug)
                debug_message("# Error recovery fails");
            return false;
        }

        /*
         * read ahead to create lookahead we can parse multiple times
         */
        read_lookahead();

        /*
         * repeatedly try to parse forward until we make it the required dist
         */
        for (;;) {
            /* try to parse forward, if it makes it, bail out of loop */
            if (debug)
                debug_message("# Trying to parse ahead");
            if (try_parse_ahead(debug)) {
                break;
            }

            /* if we are now at EOF, we have failed */
            if (lookahead[0].sym == EOF_sym()) {
                if (debug)
                    debug_message("# Error recovery fails at EOF");
                return false;
            }

            /* otherwise, we consume another Symbol and try again */
            // BUG FIX by Bruce Hutton
            // Computer Science Department, University of Auckland,
            // Auckland, New Zealand.
            // It is the first token that is being consumed, not the one
            // we were up to parsing
            if (debug)
                debug_message("# Consuming Symbol #" + lookahead[0].sym);
            restart_lookahead();
        }

        /* we have consumed to a point where we can parse forward */
        if (debug)
            debug_message("# Parse-ahead ok, going back to normal parse");

        /*
         * do the real parse (including actions) across the lookahead
         */
        parse_lookahead(debug);

        /* we have success */
        return true;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Determine if we can shift under the special error Symbol out of the state
     * currently on the top of the (real) parse stack.
     */
    protected boolean shift_under_error() {
        /* is there a shift under error Symbol */
        return get_action(((Symbol) stack.peek()).parse_state, error_sym()) > 0;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Put the (real) parse stack into error recovery configuration by popping the
     * stack down to a state that can shift on the special error Symbol, then doing
     * the shift. If no suitable state exists on the stack we return false
     *
     * @param debug should we produce debugging messages as we parse.
     */
    protected boolean find_recovery_config(boolean debug) {
        Symbol error_token;
        int act;

        if (debug)
            debug_message("# Finding recovery state on stack");

        /*
         * Remember the right-position of the top symbol on the stack
         */
        Symbol right = ((Symbol) stack.peek());// TUM 20060327 removed .right
        Symbol left = right;// TUM 20060327 removed .left

        /* pop down until we can shift under error Symbol */
        while (!shift_under_error()) {
            /* pop the stack */
            if (debug)
                debug_message("# Pop stack by one, state was # " + ((Symbol) stack.peek()).parse_state);
            left = ((Symbol) stack.pop()); // TUM 20060327 removed .left
            tos--;

            /* if we have hit bottom, we fail */
            if (stack.empty()) {
                if (debug)
                    debug_message("# No recovery state found on stack");
                return false;
            }
        }

        /*
         * state on top of the stack can shift under error, find the shift
         */
        act = get_action(((Symbol) stack.peek()).parse_state, error_sym());
        if (debug) {
            debug_message("# Recover state found (#" + ((Symbol) stack.peek()).parse_state + ")");
            debug_message("# Shifting on error to state #" + (act - 1));
        }

        /* build and shift a special error Symbol */
        error_token = getSymbolFactory().newSymbol("ERROR", error_sym(), left, right);
        error_token.parse_state = act - 1;
        error_token.used_by_parser = true;
        stack.push(error_token);
        tos++;

        return true;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Lookahead Symbols used for attempting error recovery "parse aheads".
     */
    protected Symbol lookahead[];

    /**
     * Position in lookahead input buffer used for "parse ahead".
     */
    protected int    lookahead_pos;

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Read from input to establish our buffer of "parse ahead" lookahead Symbols.
     */
    protected void read_lookahead() throws java.lang.Exception {
        /* create the lookahead array */
        lookahead = new Symbol[error_sync_size()];

        /* fill in the array */
        for (int i = 0; i < error_sync_size(); i++) {
            lookahead[i] = cur_token;
            cur_token = scan();
        }

        /* start at the beginning */
        lookahead_pos = 0;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Return the current lookahead in our error "parse ahead" buffer.
     */
    protected Symbol cur_err_token() {
        return lookahead[lookahead_pos];
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Advance to next "parse ahead" input Symbol. Return true if we have input to
     * advance to, false otherwise.
     */
    protected boolean advance_lookahead() {
        /* advance the input location */
        lookahead_pos++;

        /* return true if we didn't go off the end */
        return lookahead_pos < error_sync_size();
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Reset the parse ahead input to one Symbol past where we started error
     * recovery (this consumes one new Symbol from the real input).
     */
    protected void restart_lookahead() throws java.lang.Exception {
        /* move all the existing input over */
        for (int i = 1; i < error_sync_size(); i++)
            lookahead[i - 1] = lookahead[i];

        /* read a new Symbol into the last spot */
        // BUG Fix by Bruce Hutton
        // Computer Science Department, University of Auckland,
        // Auckland, New Zealand. [applied 5-sep-1999 by csa]
        // The following two lines were out of order!!
        lookahead[error_sync_size() - 1] = cur_token;
        cur_token = scan();

        /* reset our internal position marker */
        lookahead_pos = 0;
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Do a simulated parse forward (a "parse ahead") from the current stack
     * configuration using stored lookahead input and a virtual parse stack. Return
     * true if we make it all the way through the stored lookahead input without
     * error. This basically simulates the action of parse() using only our saved
     * "parse ahead" input, and not executing any actions.
     *
     * @param debug should we produce debugging messages as we parse.
     */
    protected boolean try_parse_ahead(boolean debug) throws java.lang.Exception {
        int act;
        short lhs, rhs_size;

        /* create a virtual stack from the real parse stack */
        virtual_parse_stack vstack = new virtual_parse_stack(stack);

        /* parse until we fail or get past the lookahead input */
        for (;;) {
            /*
             * look up the action from the current state (on top of stack)
             */
            act = get_action(vstack.top(), cur_err_token().sym);

            /* if its an error, we fail */
            if (act == 0)
                return false;

            /* > 0 encodes a shift */
            if (act > 0) {
                /* push the new state on the stack */
                vstack.push(act - 1);

                if (debug)
                    debug_message("# Parse-ahead shifts Symbol #" + cur_err_token().sym + " into state #" + (act - 1));

                /*
                 * advance simulated input, if we run off the end, we are done
                 */
                if (!advance_lookahead())
                    return true;
            }
            /* < 0 encodes a reduce */
            else {
                /*
                 * if this is a reduce with the start production we are done
                 */
                if ((-act) - 1 == start_production()) {
                    if (debug)
                        debug_message("# Parse-ahead accepts");
                    return true;
                }

                /* get the lhs Symbol and the rhs size */
                lhs = production_tab[(-act) - 1][0];
                rhs_size = production_tab[(-act) - 1][1];

                /* pop handle off the stack */
                for (int i = 0; i < rhs_size; i++)
                    vstack.pop();

                if (debug)
                    debug_message("# Parse-ahead reduces: handle size = " + rhs_size + " lhs = #" + lhs + " from state #" + vstack.top());

                /* look up goto and push it onto the stack */
                vstack.push(get_reduce(vstack.top(), lhs));
                if (debug)
                    debug_message("# Goto state #" + vstack.top());
            }
        }
    }

    /*
     * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     */

    /**
     * Parse forward using stored lookahead Symbols. In this case we have already
     * verified that parsing will make it through the stored lookahead Symbols and
     * we are now getting back to the point at which we can hand control back to the
     * normal parser. Consequently, this version of the parser performs all actions
     * and modifies the real parse configuration. This returns once we have consumed
     * all the stored input or we accept.
     *
     * @param debug should we produce debugging messages as we parse.
     */
    protected void parse_lookahead(boolean debug) throws java.lang.Exception {
        /* the current action code */
        int act;

        /* the Symbol/stack element returned by a reduce */
        Symbol lhs_sym = null;

        /* information about production being reduced with */
        short handle_size, lhs_sym_num;

        /* restart the saved input at the beginning */
        lookahead_pos = 0;

        if (debug) {
            debug_message("# Reparsing saved input with actions");
            debug_message("# Current Symbol is #" + cur_err_token().sym);
            debug_message("# Current state is #" + ((Symbol) stack.peek()).parse_state);
        }

        /*
         * continue until we accept or have read all lookahead input
         */
        while (!_done_parsing) {
            /* current state is always on the top of the stack */

            /*
             * look up action out of the current state with the current input
             */
            act = get_action(((Symbol) stack.peek()).parse_state, cur_err_token().sym);

            /* decode the action -- > 0 encodes shift */
            if (act > 0) {
                /* shift to the encoded state by pushing it on the stack */
                cur_err_token().parse_state = act - 1;
                cur_err_token().used_by_parser = true;
                if (debug)
                    debug_shift(cur_err_token());
                stack.push(cur_err_token());
                tos++;

                /*
                 * advance to the next Symbol, if there is none, we are done
                 */
                if (!advance_lookahead()) {
                    if (debug)
                        debug_message("# Completed reparse");

                    /* scan next Symbol so we can continue parse */
                    // BUGFIX by Chris Harris <ckharris@ucsd.edu>:
                    // correct a one-off error by commenting out
                    // this next line.
                    /* cur_token = scan(); */

                    /* go back to normal parser */
                    return;
                }

                if (debug)
                    debug_message("# Current Symbol is #" + cur_err_token().sym);
            }
            /* if its less than zero, then it encodes a reduce action */
            else if (act < 0) {
                /* perform the action for the reduce */
                lhs_sym = do_action((-act) - 1, this, stack, tos);

                /* look up information about the production */
                lhs_sym_num = production_tab[(-act) - 1][0];
                handle_size = production_tab[(-act) - 1][1];

                if (debug)
                    debug_reduce((-act) - 1, lhs_sym_num, handle_size);

                /* pop the handle off the stack */
                for (int i = 0; i < handle_size; i++) {
                    stack.pop();
                    tos--;
                }

                /* look up the state to go to from the one popped back to */
                act = get_reduce(((Symbol) stack.peek()).parse_state, lhs_sym_num);

                /* shift to that state */
                lhs_sym.parse_state = act;
                lhs_sym.used_by_parser = true;
                stack.push(lhs_sym);
                tos++;

                if (debug)
                    debug_message("# Goto state #" + act);

            }
            /*
             * finally if the entry is zero, we have an error (shouldn't happen here,
             * but...)
             */
            else if (act == 0) {
                report_fatal_error("Syntax error", lhs_sym);
                return;
            }
        }

    }

    /*-----------------------------------------------------------*/

    /** Utility function: unpacks parse tables from strings */
    protected static short[][] unpackFromStrings(String[] sa) {
        // Concatanate initialization strings.
        StringBuffer sb = new StringBuffer(sa[0]);
        for (int i = 1; i < sa.length; i++)
            sb.append(sa[i]);
        int n = 0; // location in initialization string
        int size1 = ((sb.charAt(n)) << 16) | (sb.charAt(n + 1));
        n += 2;
        short[][] result = new short[size1][];
        for (int i = 0; i < size1; i++) {
            int size2 = ((sb.charAt(n)) << 16) | (sb.charAt(n + 1));
            n += 2;
            result[i] = new short[size2];
            for (int j = 0; j < size2; j++)
                result[i][j] = (short) (sb.charAt(n++) - 2);
        }
        return result;
    }
}
